1. Field of the Invention
The present invention relates to an image pickup apparatus that radiates light onto a target region a plurality of times and generates a synthetic image from picked-up images of returning light thereof.
2. Description of the Related Art
In recent years, endoscopes are widely used which radiate illumination light onto a region to be observed or a region subject to image pickup from an illumination window provided at a distal end of an insertion portion and picks up an image thereof using an image pickup device provided on an observation window.
A light source section of an image pickup apparatus such as an endoscope apparatus using such an endoscope is provided with a light quantity adjusting section that adjusts an illumination light quantity of illumination light such as a diaphragm so as to pick up an image of a region subject to image pickup in a subject in a bright condition.
However, when an image of a distant region in the body cavity is picked up or an attempt is made to acquire an easy-to-observe image using illumination light of a narrow band wavelength, the illumination light quantity may be insufficient even if the diaphragm is fully opened.
For example, a first related art of Japanese Patent Application Laid-Open Publication No. 2006-314629 discloses that a spectral signal corresponding to a narrow band image acquired in the case of narrow band illumination light is generated through image processing by radiating light beams of overlapping wavelength bands a plurality of times.
On the other hand, a second related art of Japanese Patent Application Laid-Open Publication No. 11-234662 considerably changes an image pickup time (that is, shutter time) by an image pickup device between a first field and a second field, that is, changes an exposure quantity during radiation with illumination light (white color light) from a light source device and picks up images twice.
To be more specific, the image pickup device picks up images at 1/60 s for the first field and 1/240 s, which is a shutter time ¼ of 1/60 s, for the second field.
By assigning weights to and adding up the two images picked up with different shutter times, the image pickup device suppresses halation using the image picked up with the longer shutter time and the image picked up with the shorter shutter time, and generates an image of a wide dynamic range.
This related art picks up images twice while keeping open the diaphragm of the light source device and acquires an image with an enlarged dynamic range.